Inspection Technique for Spur Gears

There are different methods used within the industry for inspection of spur gears. In general, there are various parameters considered during the inspection methodology. However, two major aspects that tops the priority list are Total Composite Error (TCE) and Tooth Thickness.

 

Both these parameters can be gauzed using a roll-testing variable center distance fixture or so called “gear roll testing inspection”. There are many variety of testing fixture available, however all of these fixtures in common have two common shafts (precision centers), one fixed and other floating smooth friction guide.

 

Inspection Methodology
Gear to be inspected is mounted on shaft, while an ideal or master gear is mounted on the other shaft to match the dimensions. The mounting is placed in such a way that both gears come in contact through spring load. After the tooth is accurately meshed, the gears are rotated and tooth-to-tooth errors are accurately measured. These measurements are compared with acceptable dimensional limits. The greatest feature of this simpled methodology is that its a completely functional technique. If the center roller distance of the roll tester is accurately set, the tooth thickness can be identified.

 

Other Methodologies
There are various other methodologies for inspecting the accuracy of gear dimension. Pin roll method is amongst the most dependable techniques, specially useful in shops with limited inspection capabilities and equipments. Two wires or pins of specific diameters are positioned in diametrically opposite tooth spaces. If gears have odd number of teeth, the pins are located exactly opposite to each other. The overall measurement, from outer edge of each pin is measured. The total of this measurement is compared to predetermined valued based on acceptable tolerance.

 

Special Purpose Measurement Equipment
There are various other special purpose measurement equipment available for gear inspection. The long list includes tooth spacing gages, profile form checker and runout checkers. Other testing equipments are available for inspecting high precision gears used in automotive, aerospace and other industries.